Primary air pollutants are emitted directly from a source, such as a vehicle or factory, and include particulate matter, sulfur dioxide, nitrogen oxides, and carbon monoxide.

Vehicle emissions are a major source of air pollution in urban areas, contributing to high levels of particulate matter, nitrogen oxides, and carbon monoxide.

Ozone is a secondary air pollutant formed by the reaction of sunlight with nitrogen oxides and volatile organic compounds. It can cause respiratory problems, such as asthma and bronchitis, and contribute to smog.

The Clean Air Act is a comprehensive federal law that aims to protect air quality and public health by regulating air emissions from various sources.

Emission standards are a type of command-and-control regulation that sets specific limits on the amount of pollutants that can be emitted from a source.

A cap-and-trade system allows regulated entities to trade emission allowances, providing flexibility in meeting emission reduction targets and potentially reducing overall compliance costs.

Evaluating the effectiveness of environmental regulations for air pollution can be challenging due to a combination of factors, including lack of data, difficulty in isolating the impact of regulations, and political and economic pressures.

The NAAQS are a set of federal air quality standards that establish limits for six criteria air pollutants: particulate matter, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead.

A cap-and-trade system is a market-based instrument that sets a cap on the total amount of pollution allowed and allows regulated entities to trade emission allowances.

The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances.

Implementing and enforcing environmental regulations for air pollution can be challenging due to a combination of factors, including lack of political will, limited resources, and resistance from regulated industries.

The Clean Air Act Amendments of 1990 focused on regulating air pollution from vehicles and industrial sources, including setting new emission standards and implementing market-based instruments.

A memorandum of understanding between government and industry is an example of a voluntary agreement for air pollution control, where both parties agree to work together to reduce emissions.

Evaluating the effectiveness of voluntary agreements for air pollution control can be challenging due to a combination of factors, including lack of data, difficulty in isolating the impact of voluntary agreements, and lack of enforcement mechanisms.

Sulfur dioxide is a common air pollutant that can contribute to acid rain when it reacts with water vapor in the atmosphere to form sulfuric acid.